The presence of hydrogen cyanide (HCN) in various gaseous streams complicates removal of additional impurities, e.g., removal of H.sub.2 S or CO.sub.2, and poses problems insofar as product quality and pollution control requirements are concerned. In particular, gas streams derived from the gasification of coal generally have significant minor quantities of HCN which must be dealt with before the gas is utilized. In some cases significant quantities of COS may also be present, and these must be removed to meet the specification for total sulfur in the product gas. A gas phase catalytic treatment which removes HCN, and preferably COS as well, from coal gasification derived synthesis gas streams, with minimal water-gas shift and without generating mercaptans (such as methyl mercaptan) might have great economic value. The invention concerns such a process.